bpo-33751: Fix test_file. (GH-7378)

testModeStrings and testTruncateOnWindows were depended on
a file leaked in other tests.

Also improve cleaning up after tests.

Lib/test/test_file.py

@@ -8,6 +8,7 @@ import io
 import _pyio as pyio
 
 from test.support import TESTFN
+from test import support
 from collections import UserList
 
 class AutoFileTests:
@@ -19,7 +20,7 @@ class AutoFileTests:
     def tearDown(self):
         if self.f:
             self.f.close()
-        os.remove(TESTFN)
+        support.unlink(TESTFN)
 
     def testWeakRefs(self):
         # verify weak references
@@ -137,8 +138,12 @@ class PyAutoFileTests(AutoFileTests, unittest.TestCase):
 
 class OtherFileTests:
 
+    def tearDown(self):
+        support.unlink(TESTFN)
+
     def testModeStrings(self):
         # check invalid mode strings
+        self.open(TESTFN, 'wb').close()
         for mode in ("", "aU", "wU+", "U+", "+U", "rU+"):
             try:
                 f = self.open(TESTFN, mode)
@@ -185,7 +190,6 @@ class OtherFileTests:
         # SF bug <http://www.python.org/sf/801631>
         # "file.truncate fault on windows"
 
-        os.unlink(TESTFN)
         f = self.open(TESTFN, 'wb')
 
         try:
@@ -209,7 +213,6 @@ class OtherFileTests:
                 self.fail("File size after ftruncate wrong %d" % size)
         finally:
             f.close()
-            os.unlink(TESTFN)
 
     def testIteration(self):
         # Test the complex interaction when mixing file-iteration and the
@@ -230,7 +233,6 @@ class OtherFileTests:
         methods = [("readline", ()), ("read", ()), ("readlines", ()),
                    ("readinto", (array("b", b" "*100),))]
 
-        try:
         # Prepare the testfile
         bag = self.open(TESTFN, "wb")
         bag.write(filler * nchunks)
@@ -309,8 +311,6 @@ class OtherFileTests:
                 self.fail("read* failed after next() consumed file")
         finally:
             f.close()
-        finally:
-            os.unlink(TESTFN)
 
 class COtherFileTests(OtherFileTests, unittest.TestCase):
     open = io.open
@@ -319,11 +319,5 @@ class PyOtherFileTests(OtherFileTests, unittest.TestCase):
     open = staticmethod(pyio.open)
 
 
-def tearDownModule():
-    # Historically, these tests have been sloppy about removing TESTFN.
-    # So get rid of it no matter what.
-    if os.path.exists(TESTFN):
-        os.unlink(TESTFN)
-
 if __name__ == '__main__':
     unittest.main()